Temporal and geographic variation in parasitoid attack with no evidence for ant protection of the Melissa blue butterfly, Lycaeides melissa.

摘要

Interactions among caterpillars, ants and parasitoids have informed much of what is known about tritrophic ecological dynamics. However, detailed studies encompassing all three trophic levels are limited to relatively few natural systems. In this study, interactions of the Melissa blue butterfly, Lycaeides melissa, with mutualistic ants and parasitoids in the context of novel host plant use by the butterfly were investigated. Over the course of 2 years, 526 caterpillars and 288 ants tending caterpillars were collected from 185 plants at sites with two different native host plants and the exotic host alfalfa, for the purpose of investigating if the presence of ants was associated with reduced rates of parasitism. The abundance and diversity of parasitoids varied considerably across space and time. The presence of tending ants did not appear to reduce rates of parasitism, in contrast to a previous study of L. melissa, which found evidence of ant protection against spiders and other predators. This study has increased our understanding of ant-caterpillar-enemy interactions, and previously unobserved interactions have been documented, including at least two new host-parasitoid relationships. These findings highlight the importance of investigating ecological interactions, including interactions with other trophic levels, when studying diet breadth and ecological diversification in herbivorous insects.